Some of the images obtained by fixing a toner on a recording medium, such as paper, can reversibly switch between a chromogenic state and an achromatized state in response to temperature changes.
To achieve this effect in the related art, a toner containing a colorant which exhibits a hysteresis in a temperature-color state curve thereof, is used.
However, for the toner containing a colorant which exhibits the hysteresis, the temperature condition needs to be controlled, such that the state of the colorant does not change from the chromogenic state to the achromatized state at the time of producing the toner or at the time of fixing the toner to form the image.
Moreover, in the case of the image obtained by the toner, if an attempt is made to cause the image, which is in the achromatized state, to produce a color, the image has to be kept at a low temperature such as a temperature lower than 0° C. for a long time in some cases.